Apparatus for making porous metal parts



Nov. 14, 1944. R. P. KOEHRING APPARATUS FOR MAKING POROUS METAL PARTS 2 Sheets-Sheet 1 Filed Oct. 17. 1941 INVENTOR I Mafia Enemy HIS ATTORN S Nov- 1 194 R. P. KOEHRING APPARATUS FOR MAKING POROUS METAL PARTS Filed Oct. 17, 1941 2 Sheets$heet 2 INVENTOR Rafa/m f? flaabnizzq Hl ATTORNEYfi Patented Nov. 14, 1944 APPARATUS FOR MAKING POROUS 1 METAL PARTS Roland P. Koehring, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a

"corporation of Delaware Application October 17, 1941, Serial No. 415,446

1 Claim.

This invention relates to an'apparatus for heating metal powder and is particularly concerned with an apparatus wherein articles may be formed from metal powder by hot pressing.

An object of the invention is to provide an apparatus for continuously producing agglomerated charges of powdered metals which may be hot pressed to the desired shape.

A further object of the invention is to provide an apparatus for progressively heating a portion of the charge of powdered metal to an aggiomerating temperature and then progressively hot pressing said portion while simultaneously causing another portion of said charge to become heated.

Further objects and advantages of the present invention will be apparent from the following description, reference being bad to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

Fig. 1 is a diagrammatic view of apparatus used to carry out the invention disclosed herein showing the charge of metal powder in the furnace at the start of a cycle of operation.

Fig. 2 shows the second step of the process wherein an agglomerated portion of the charge has been ejected from the furnace.

Fig. 3 shows the ejectedportion being cut off from the remainder of the charge in the furnace and wherein the portion is ready to fall into the die.

Fig. 4 shows the cut-off portion being hot pressed in the die.

Fig. 5 shows the formed article after the hot pressing operation.

Fig. 6 is a view taken on the line 8-45 of Fig. 5 showing the ejecting means utilized to remove the hot pressed article from the die.

Fig. 7 is a fragmentary view of the ejecting.

means showing the finished article dropping therefrom. 3

Referring to the drawings and particularly'to Fig. 1, is a horizontally disposed tube ot-substantial length formed from graphite, alumina, silica or other suitable refractory material. Around one end of the tube 20 is disposed a heating coil 22 which is connected to a suitable current source for supplying an electro-magnetic field within the coil whereb metallic material within the tube is heated inductively within the area covered by said coil. In the opposite end of the tube 20 is disposed a piston 24 capabl of reciprocation within the limits shown in Figs. 1 and 2. Above piston 24 an opening 28 is provided whereby powder 28 from a supply hopper 30 may fall into the chamber within tube 20 and form the charge 32. Piston 24 acts as a slide valve across the opening 28 whereby when the piston .is in the forward position the opening 26 is closed and the charge 32 is pressed under suflicient pressure from piston 24 to cause a portion thereof as 34 in Fig. 2 to be ejected or extruded from the tube 20. Upon the reverse movement of piston 24 additional powder 28 falls through the opening 26 into the chamber to replenish the amount of metal in portion 34 which has been ejected from the tube. Thus upon each reciprocation of piston 24 a measured portion 34 of the charge 32 is ejected from the heating chamber.

The powdered metal in charge 32 is heated inductively within the field of the coil 22 to a temperature sufficient to cause the powdered metal particles to at least partially sinter and thereby become agglomerated into a self-sustaining mass whereby the portion 34 ejected from the tube while hot, for example, if iron powder is being used at a temperature of between 1800 and 2100" F. remains attached to the remainder of the.

charge in the tube. After the inward limit of reciprocation of piston 24 has been reached, a cut-ofi blade 38 is moved downwardly as shown in Fig. 3 and cuts off the ejected portion of the metal powder 34 which is self-adhering in character. Portion 34 then drops into a cavity 38 in an ejecting means 40. At this point an upper punch 42 moves downwardly and presses the portion 34 under sufficient pressure to cause the lower punch 44 to recede to a stop, thereby forming a die cavity 46. At this point additional pressure on the upper punch 42 causes the charge of agglomerated metal powder to be pressed to the exact size and shape of the cavity and form a strong metal article 48 which has a low degree of porosity. After the formation of the article 48 is complete, punch 42 recedes and punch 44 raises the article into the cavity 38 whereupon the elector rotates and moves the article out of the pressing chamber and into either a cooling chamber (not shown) or into an oil bath.

It is preferred that the pressing chamber designated at 50 and the cooling chamber, if used, are both maintained under non-oxidizing condition since the article 48 which is formed from the cutoff portion 34 of metal powder is maintained at a high temperature in the chamber 58, and if any oxidizing gases are present therein, oxidation of the metal would occur, which is usually undesirable.

If desired, a baflle 52 may be provided within the chamber 50, shielding the upper punch from the heat of the furnace. Likewise the punch may be water-cooled to prevent over-heating thereof and in any event should be made from heat-resistlng steel.

Another embodiment of the invention comprehends the formation of annuli from the same type of apparatus wherein a core may be placed within the heating chamber which extends past the heated portion thereof slightly so that the powder, divides as it passes the core and the annulus portions are cut off and fall into the die. In this instance, it is preferable to have a pilot on one of the punch members which has the desired diameter for the finished annulus. Likewise the core should have a larger diameter than the desired finished diameter so that when hot pressing occurs the charge of agglomerated powder may be pressed to shape.

It is apparent that other shapes may be made in apparatus of this character wherein the shape of the heating chamber can be varied together with the shape of the piston which reciprocates therein; for example, hexagons, Us, squares or any other type of cross section may be formed either with or without apertures therein.

In each instance the charge which is ejected from the furnace consists of a measured quantity of metal powder which is agglomerated and has been elevated to the desired pressing temperature. This charge does not necessarily have to be the exact shape or size of the finished article and therefore it is preferable to make the charge of less diameter than the finished articl in most cases.

Instead of inductively heating the charge, resistance heating may be resorted to or the chamber may be heated externally by gas or other conventional heating mediums. However, in these latter cases the action of the furnace is slowed down considerably since it is necessary to bring the charge of metal powder to be ejected to a predetermined temperature prior to ejecting and it is apparent that the charge must be held in the heating zone a suflicient length of time to accomplish this end. It is for this reason that induction heating is preferred since it is the most rapid, as only short time need elapse to cause the metal powder to reach the desired temperature. The temperature to which the metal powder is heated is well known to those skilled in the art and varies in accordance with the particular metal powder being heated. In this instance it is only necessary to heat the powder to a temperature sufiicient to cause the powder to coalesce and to become self-sustaining, likewise the pressures used for hot pressing may vary in accordance with the result desired. If a high porosity piece is desired the pressure may be re-' duced to accomplish this end; likewise if a highly compressed piece of considerable strength is required this'pressure may be increased; therefore it is best to arrive at the exact heating temperature and hot pressing pressures by trial for the particular piece required.

Attention is directed to copending application. Serial No. 393,610, Method and apparatus for making articles from metal, filed May 15, 1941, filed by John T, Marvin, which discloses another method for hot-pressing articles wherein measured increments'of a charge of powder are utilized to form the article so that the process is a continuous one.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted, all coming within the scope of the claim which follows.

What is claimed is as follows:

Apparatus for forming strong, highly compressed articles from metal powders, comprising in combination an elongated heating chamber of uniform cross section including adjacent an open end thereof an induction heating coil capable of agglomerating a portion only of the metal powder charge into said chamber, a piston disposed at the other end of said chamber and capable of reciprocation for ejecting a predetermined portion only of the hot agglomerated metal pow der from said chamber upon each inward stroke thereof, supply means for supplying additional metal powder to the chamber on each outward stroke of said piston whereby the portion. of agglomerated metal powder ejected from the chamher by the inward stroke of the piston is replenished, out 01f means disposed externally of the heating end of said chamber for cutting off the ejected metal powder, said out off means being synchronized to operate on the outward stroke of said piston, a die having a desired configuration of the article to be formed, means for conveying the hot agglomerated portion cut off by the cut off means to said die, compressingmeans for compacting the cut oil portion While hot in said die to form an article of high density, strength and of the desired shape, ejecting means for ejecting the compacted article from said die,

said compressing meahs and ejecting means being synchronized to operate upon each cycle of operation of the piston and cut oil means, and supply means for supplying a controlled atmosphere around the heating end of said chamber and around the die, compressing means and ejecting means whereby the portion of metal powder ejected from the chamber is at no time subjected to the action of the air until after the compacting step has been completed.

' ROLAND P. KOEI-IRING. 

